The present invention relates to a device for preventing evaporation of fuel generally referred to as canister and adapted to catch fuel evaporated from the fuel supplying system including fuel tank, carburetor and so forth of a vehicle, thereby to avoid air pollution by the evaporated fuel.
Hitherto, such fuel evaporation preventing devices have been proposed and broadly used as incorporating a canister having a fuel absorbent which absorbs the evaporated fuel and releases the same during operation of the engine thereby to supply the engine with the released fuel. Examples of the fuel evaporation preventing device of the kind described as shown in Japanese Patent Publication Nos. 19729/1978, and 45748/1980. Devices are proposed also for allowing the utilization of an large portion as possible of the absorbent by means of a flow detector which serves to deflect and diversify the flow of the evaporated fuel to make efficient use of large portion of the absorbent. Examples of such system as shown in, for example, Japanese Patent Publication No. 59909/1982 and Japanese Patent Laid-Open Nos. 69455/1981 and 157053/1982.
For instance, the canister shown in Japanese Patent Laid-Open Publication No. 157053/1982 has an absorbent and a flow deflector housed by a casing. This flow defector includes a conical portion and a tubular portion connected to the conical portion. The tubular portion is provided at its upper end with a check valve. In this canister, the fuel vapor evaporated from the fuel tank during suspension of engine operation is introduced through a fuel vapor introduction pipe into the absorbent of the canister. The fuel vapor flows obliquely upwardly along the inner surface of the conical portion of the flow defector and flows over the upper brim of the conical portion. The fuel then flows downwardly. This downward flow of the fuel vapor, however, does not come into the portion of the absorbent adjacent to the conical portion and the tubular portion of the flow deflector, because it tends to flow along the shortest path which minimizes the flow resistance. Accordingly, it can not make efficient use of the portion of the absorbent around the conical and tubular portions of the flow deflector.
Another problem of this known arrangement is that the material of the absorbent above the check valve tends to be pulverized due to the vibration to cause troubles such as sealing failure and/or stick of the check value. The sealing failure of the check valve may cause a leak of the fuel vapor therethrough to a second diffusion chamber, from which the fuel vapor is relieved to the atmosphere without being absorbed by the absorbent. On the other hand, the stick of the check value causes a problem that, since the air sucked through the atmospheric port in the bottom of the canister flows detouring the flow deflector, the fuel vapor caught by the portion of the absorbent in the conical portion is not released from the absorbent.
Furthermore, it is to be noted that the flow deflector is rendered complicated in construction and expensive due to the use of the check valve.
Thus, the conventional fuel evaporation preventing device suffers from various disadvantages such as the complicated construction, only partial use of the flow deflector which is intended for diversifying the flow of fuel and only limited regeneration efficiency of the canister.